title: Complex between α-bungarotoxin and an α7 nicotinic receptor ligand-binding domain chimaera.
abstract: To identify high-affinity interactions between long-chain α-neurotoxins and nicotinic receptors, we determined the crystal structure of the complex between α-btx (α-bungarotoxin) and a pentameric ligand-binding domain constructed from the human α7 AChR (acetylcholine receptor) and AChBP (acetylcholine-binding protein). The complex buries ~2000 Å² (1 Å=0.1 nm) of surface area, within which Arg³⁶ and Phe³² from finger II of α-btx form a π-cation stack that aligns edge-to-face with the conserved Tyr¹⁸⁴ from loop-C of α7, while Asp³⁰ of α-btx forms a hydrogen bond with the hydroxy group of Tyr¹⁸⁴. These inter-residue interactions diverge from those in a 4.2 Å structure of α-ctx (α-cobratoxin) bound to AChBP, but are similar to those in a 1.94 Å structure of α-btx bound to the monomeric α1 extracellular domain, although compared with the monomer-bound complex, the α-btx backbone exhibits a large shift relative to the protein surface. Mutational analyses show that replacing Tyr¹⁸⁴ with a threonine residue abolishes high-affinity α-btx binding, whereas replacing with a phenylalanine residue maintains high affinity. Comparison of the α-btx complex with that coupled to the agonist epibatidine reveals structural rearrangements within the binding pocket and throughout each subunit. The overall findings highlight structural principles by which α-neurotoxins interact with nicotinic receptors.
authors.affiliation: Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, MN 55902, U.S.A.
authors.forename: Sun
authors.initials: S
authors.lastname: Huang
authors.affiliation: Molecular and Computational Biology, Departments of Biological Sciences and Chemistry, University of Southern California, 1050 Childs Way, Los Angeles, CA 90089-2910, U.S.A.
authors.forename: Shu-Xing
authors.initials: SX
authors.lastname: Li
authors.affiliation: Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, MN 55902, U.S.A.
authors.forename: Nina
authors.initials: N
authors.lastname: Bren
authors.affiliation: Molecular and Computational Biology, Departments of Biological Sciences and Chemistry, University of Southern California, 1050 Childs Way, Los Angeles, CA 90089-2910, U.S.A.
authors.forename: Kevin
authors.initials: K
authors.lastname: Cheng
authors.affiliation: Molecular and Computational Biology, Departments of Biological Sciences and Chemistry, University of Southern California, 1050 Childs Way, Los Angeles, CA 90089-2910, U.S.A.
authors.forename: Ryan
authors.initials: R
authors.lastname: Gomoto
authors.affiliation: Molecular and Computational Biology, Departments of Biological Sciences and Chemistry, University of Southern California, 1050 Childs Way, Los Angeles, CA 90089-2910, U.S.A.|Norris Comprehensive Cancer Center, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, U.S.A.
authors.forename: Lin
authors.initials: L
authors.lastname: Chen
authors.affiliation: Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, MN 55902, U.S.A.|Department of Neurology, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, MN 55902, U.S.A.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Sine
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000737:chemistry / Q000378:metabolism; D002038:Bungarotoxins / Q000737:chemistry / Q000378:metabolism*; D017838:Bungarus; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003039:Cobra Neurotoxin Proteins / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008024:Ligands; D008195:Lymnaea; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009498:Neurotoxins / Q000737:chemistry / Q000378:metabolism*; D018722:Nicotinic Agonists / Q000737:chemistry / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D011725:Pyridines / Q000737:chemistry / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D030162:Reptilian Proteins / Q000737:chemistry / Q000378:metabolism*; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: C428944:AChBP protein, Lymnaea; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002038:Bungarotoxins; D002352:Carrier Proteins; C579167:Chrna7 protein, human; D003039:Cobra Neurotoxin Proteins; D008024:Ligands; D050505:Mutant Proteins; D009498:Neurotoxins; D018722:Nicotinic Agonists; D010446:Peptide Fragments; D011725:Pyridines; D011978:Receptors, Nicotinic; D011993:Recombinant Fusion Proteins; D030162:Reptilian Proteins; D064569:alpha7 Nicotinic Acetylcholine Receptor; C025154:alpha-cobratoxin; C082748:epibatidine